In the design of inking mechanisms for rotary printing presses it is the practice to provide means for vibrating or axially reciprocating the ink drums to thereby more effectively distribute the ink into a uniform, thin film prior to its reaching the printing plate. Various types of vibrating mechanisms have been devised in the past, most of which have proved to be relatively effective for the purpose. However, the known devices are relatively complex and thus expensive to manufacture and maintain. Moreover, most of the devices are difficult and time consuming to adjust for the purpose of varying the amplitude of the reciprocating motion because they are fully enclosed in oil tight compartments and are only accessible by removing cover plates from the frame. A further disadvantage resides in the fact that a separate adjustment must be effected for each ink drum.